摘要
Trace La element was introduced in Al-20Mg_(2)Si composites to regulate the microstructure and corrosion performance.The modification mechanism of trace La and the corrosion behavior of the newly developed composites were systematically investigated by thermal analysis,microstructural observations and electrochemical tests.Our study reveals that the addition of only 0.10%La can refine the size of the primary Mg_(2)Si phase from 77.6 to 26.7μm,modify its morphology from a coarse dendrite to a fine truncated octahedron and reduce the corrosion current density from 5.96μA cm^(-2) to 3.03μA cm^(-2).Trace La refines the primary Mg_(2)Si phase size by forming a tiny LaAlSi phase which can provide effective heterogeneous nuclei for the primary Mg_(2)Si phase during solidification.Excess La atoms can selectively adsorb on the{100}facets of the primary Mg_(2)Si phase and suppress the preferential growth of the Mg_(2)Si phase,eventually resulting in the morphological transition of the primary Mg_(2)Si phase from dendrite to truncated octahedron shape.The enhanced corrosion resistance of the La micro-alloyed Al-20Mg_(2)Si composites can be attributed to the formation of stronger protective surface oxide films and finer primary Mg_(2)Si phase.The protective oxide films can effectively hinder the penetration of the corrosive medium and the finer primary Mg_(2)Si phase can weaken the localized corrosion tendency of the Al-Mg_(2)Si composites.
基金
supported by the National Natural Science Foundation of China(Nos.52201051 and 52201295)。
